1. Field of the Invention
This invention relates to a pressure vessel, in particular an aerosol can for containing gas under pressure, especially flammable gases such as butane, isobutane and propane. The pressure vessel comprises a container, an open celled foam, preferably reticulated, a pressure relief system, and an opening in the container for discharge of gas or contents. The foam and the pressure relief system in combination substantially reduce the likelihood of flareout from the vessel in use and in storage. When stored, the vessel design is such that the buildup of heat and pressure in the event of fire, such that the cans explode and become dangerous projectiles is substantially reduced or eliminated.
2. Description of the Related Art
The use of two-piece and three-piece aerosol cans for flammable material to be delivered under pressure is known. Containers of this type have been used for the packaging of a number of gases, but in the flammable liquified gas area, only butane and isobutane have been approved for packaging in such containers. Some aerosol containers are approved for use with non-flammable gas such as liquified chlorodifluoromethane (HCFC), having a pressure of 113.6 PSI-G (21.13 Bar) at 70.degree. F. (21.11.degree. C.) and 300 PSI-G (21.13 Bar) at 130.degree. F. (54.4.degree. C.). In a fire a non-flammable gas container reacts the same way as does a container of flammable gas, except that it does not burn. Butane and isobutane are considered low pressure liquified hydrocarbon gases, with pressures of 17 and 32 PSI-G, respectively, at 70.degree. F. (21.11.degree. C.). For propane, the pressure is 108-110 PSI-G at 70.degree. F. (21.11.degree. C.). Currently propane is not approved for packaging in any aerosol container. Propane is approved for use in one lb. and up cylinders which containers are subject to government regulations in both Canada and the United States which differ from the regulations governing aerosol containers. In the U.S., the Department of Transport is the governing authority, while in Canada it is Transport Canada. These government authorities and others such as the National Fire Protection Agencies regulate under penalty of law. Underwriters Laboratories also sets standards for such products, but approval is imposed as a result of commercial pressures.
Subsequent to the development of two- and three-piece aerosol cans, it became common to equip such cans with a pressure relief system when they were used to contain flammable gases with pressures of up to 45 PSI-G at 70.degree. F. (21.11.degree. C.). Examples of such systems are the rim vent system and the bottom vent system. These systems were meant to preclude explosion of these cans when subjected to high temperatures. These systems will be described in greater detail subsequently.
However, there remained an unsolved problem with the use of aerosol cans filled with liquified petroleum gas. This occurred in use, when the can was inverted and a welding torch or like appliance was secured to an actuator valve. The liquid phase of the gas moved to the actuator valve opening in the can, rather than remaining in the lower portion of the can, thus flooding the actuator valve when activated. In such instance, the liquid phase of the liquified gas surged to the actuator valve opening, frequently creating a condition called flareout which could cause a dangerous fire situation. In fact, it is quite common for handbooks associated with devices of this type to include a warning that the aerosol vessel or container should not be inverted when used.
Attempts have been made over the years to find a solution to flareout by introducing to the attached appliances, parts, such as diaphragms and back pressure valves. The diaphragm was the least expensive but the most ineffective. The back pressure relief valve was considered to be effective, but it was expensive to make, insert and test, and unfortunately, when inserted into the appliance, it wasn't always 100% failsafe. These solutions were associated with the appliance and not the fuel container.
It was also observed that when aerosol vessels or cans equipped with a pressure relief system became overheated, the rapidly expanding liquified petroleum gas (LPG), being one mass in the can and under pressure, forced the dome to evert and on a rim vent can, the vents to fracture as the can pressure increased. In the case of bottom vent pressure relief systems, which usually comprise a coin-shaped score mark on the concave bottom of the can, the score mark fractures as the can heats up and the gas expands to just below the burst pressure of the can. When this occurs and the pressure relief system of the can opens, allowing the gas to escape, the released gas then ignites to form a fireball. In a warehouse fire, where a quantity of aerosol cans without either device might be stored, the fireball created could become quite large and the force propelled on by the fireball could cause not only undue fire damage, but also structural damage to a building. In a situation where such cans had a pressure relief system, it has been found also that the flames from the fireball were often sucked back into the cans before the entire amount of the gas had been exhausted, creating violent explosions with the cans becoming projectiles and causing more than fire damage to property.
The use of foam in fuel tanks and fuel storage containers to prevent explosions is well known having been used extensively in military aircraft fuel tanks and in racing cars. The following patents typify such applications.
______________________________________ U.S. Pat. No. Issue Date Inventor(s) ______________________________________ 3,567,536 March 2, 1971 William W. Wickersham, Jr. 3,703,976 Nov. 28, 1972 William L. Hughes, et al 3,708,330 Jan. 2, 1973 G. B. Harr 4,294,279 Oct. 13, 1981 Harold W. G. Wyeth 4,328,901 May 11, 1982 Robert J. Gunderman, et al 4,764,408 Aug. 16, 1988 Donald R. Stedman, et al 4,765,458 Aug. 23, 1988 Edith M. Flanigen 4,927,045 May 22, 1990 Helmut J. Lichka ______________________________________
None of these patents describes an aerosol container for gases of any type.
It is understood that there have been on the market, aerosol cans for butane and isobutane (propane may not be used) which contain foam for the purpose of overcoming surge of the liquid phase of the gas when the aerosol can is inverted. Such products are said to be supplied by Sakae Seiki Co. Ltd. and Yoshinaga Prince Co. Ltd., both of Japan. The use of foam in a can has proved to be far more effective than other methods in eliminating surge problems when the full fuel can is inverted. However, such cans have not incorporated a pressure relief system, which meant that although the problem of surging or flaring was avoided, the difficulty of storing aerosol containers holding flammable materials under pressure was not. In one of these designs, the foam is a reticulated foam and has a centrally located hole extending from the top to halfway down the foam. The hole received a double dip tube attached to the actuator valve which acts to reduce or eliminate surge or flareout. The primary purpose of the double dip tube is to stop surge and allow time for the liquid phase of gas to vapourize when the can is inverted. The function of the foam is secondary as it retains the liquid phase of the gas within its cell structure, stopping the surge to the actuator valve when the can is inverted. Without the foam the double dip tube would rest in the liquid gas phase. This design was found to be too expensive for use in a can of fuel and was discontinued. There are also on the market small aerosol packages of flammable gas, such as butane and isobutane, as well as very small containers of butane for curling irons, small torches and lighters.